Cryptococcus neoformans (C. neoformans) is an encapsulated yeast mainly responsible for meningitis/meningocephalitis in patients infected with HIV. For areas of the world where HIV is endemic, C. neoformans is the most common cause of culture-positive meningitis (e.g., Zimbabwe, Malawi, and Cambodia). C. neoformans is commonly acquired by inhalation. Extrapulmonary dissemination can lead to infection of the bloodstream and subsequent hematogenous dissemination to target organs, most commonly resulting in meningoencephalitis. Several lines of evidence from experimental mouse models of cryptococcal meningitis indicate that C. neoformans invasion into the brain follows fungemia, and cerebral capillaries, not the choroid plexus, are the portal of entry. It is, however, unclear how C. neoformans traverses the blood-brain barrier. We have developed the in vitro model of the blood-brain barrier by isolation and cultivation of human brain microvascular endothelial cells (HBMEC). Our primary HBMEC, upon cultivation on collagen-coated Transwell inserts, form a continuous lining of endothelial cells and exhibit transendothelial electrical resistance of 300-600 ohms/cm2, a unique property of the brain microvascular endothelial monolayer. Our preliminary findings revealed that C. neoformans strains were able to traverse primary HBMEC monolayers without any change in the integrity of HBMEC monolayers. Based on this novel finding, we would like to examine the following specific aims: 1. To examine the role of host cell actin cytoskeleton rearrangements and related signal transduction pathways that are involved in C. neoformans traversal of primary HBMEC monolayers. 2. To assess how C. neoformans traverses primary HBMEC monolayers. The information derived from this exploratory application should provide the information on the mechanisms involved in C. neoformans traversal of HBMEC monolayers and will be the basis of future investigations to characterize microbial-host interactions that are relevant to the pathogenesis of cryptococcal meningitis/meningoencephalitis.